1. Field of the Invention
The present invention relates to projection lenses and in particular to a zoom projection lens in which one or more elements is movable to provide variable magnification.
2. Description of the Prior Art
Zoom lenses for use in photographic apparatus are well known. Moreover, high relative aperture zoom lenses have also been known for many years. However, most prior art zoom lenses, particularly those characterized by a high relative aperture, are relatively complex in construction and require costly high index glasses to provide good aberration correction. Moreover, many such zoom lenses have two or more movable elements, requiring adequate room for the relative movement of the elements and accurate mounting of the elements. Use of high index glasses also makes the zoom lens relatively expensive to produce because of the cost of each glass, as well as the manufacturing cost of each individual glass element along with assembly of the final lens.